Field of the Disclosure
This disclosure relates generally to catalyst materials for three-way catalyst (TWC) applications, and more particularly, to a synergized platinum group metal (PGM) TWC catalyst configuration for reduction of emissions from engine exhaust systems.
Background Information
The efficiency of a three-way catalyst (TWC) converter for treating the exhaust gas of an engine is affected by the ratio of air to fuel (A/F) supplied to the engine. At stoichiometric A/F ratio, combustion can yield complete consumption of the fuel because catalytic conversion efficiency is high for both oxidation and reduction conversions. Maintenance of effective fuel consumption requires the utilization of fuel control systems that are designed to keep the A/F ratio within a narrow range that is close to the stoichiometric ratio. The fluctuations of the A/F ratio are called A/F perturbations.
Standard TWC Systems
FIG. 1 is a block diagram illustrating a conventional Three Way Catalyst (TWC) system portion of an engine system that includes a standard platinum group metals (PGM) close-coupled catalyst (CCC) having PGM and Ce-based oxygen storage and an PGM underfloor catalyst. In FIG. 1, engine system 100 includes engine 104 and TWC system 110. TWC system 110 further includes standard PGM CCC 102, PGM underfloor catalyst 106, and analysis point P 108. In FIG. 1, engine 104 is mechanically coupled to and in fluidic communication with TWC system 110. In TWC system 110, standard PGM CCC 102 is mechanically coupled to and in fluidic communication with PGM underfloor catalyst 106.
In FIG. 1, point P 108 is located at the inlet port of standard PGM CCC 102. At point P 108, air to fuel (A/F) perturbations are generated when the initial lean interval of an A/F ratio is greater than the stoichiometric value. This initial lean interval is followed by a series of rich intervals of A/F ratio that are lower than the stoichiometric value. The series of rich intervals of A/F ratios alternate with lean intervals of A/F ratios because the engine control system is reacting to exhaust gas sensors (not shown) located prior to TWC system.
In conventional TWC systems, an efficiency value for the catalytic conversion capability of standard PGM CCC 102 is determined on the basis of the number of the A/F perturbations following the initial lean interval. Since the A/F perturbations typically possess high amplitudes at low frequencies at analysis point P 108, the catalytic conversion efficiency of standard PGM CCC 102 is affected by these wide swings in A/F ratio from engine 104.
Accordingly, there is a need for TWC systems having improved performance meeting stringent governmental regulations for automotive exhaust systems. There is also a need to do so in a cost-effective manner.